This application claims the priority of German application 197 47 287.7, filed in Germany on Oct. 25, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process for open-end spinning, in which (i) at least one sliver is opened into single fibers; (ii) parallel single fibers extending in the direction of motion, form a wide fiber veil, (iii) the fiber veil is transported by means of a moving collecting surface to a transfer point, (iv) at the transfer point the single fibers are transferred from the collecting surface to a transporting surface, whereby the current position of the single fibers is essentially maintained, (v) the single fibers are transported by means of the transporting surface to a spinning line, which extends on the transporting surface transversely to its direction of motion; and (vi) the single fibers are spun into a yarn along the spinning line, which yarn is withdrawn in its longitudinal direction.
A spinning process of this type is described in U.S. Pat. No. 5,768,879. In this process, a wide fiber veil is formed from parallel fibers extending in the direction of motion, whereby the number of fibers in the fiber veil corresponds to the number of fibers later found in the yarn cross section, as long as no subsequent doubling occurs. Directly after the sliver has been opened into single fibers, that is, at a point at which the single fibers have not yet reached a high speed, the fiber veil is taken up at a controlled speed by a mechanical collecting surface. This controlled speed permits the single fibers to remain constantly stretched without any crinkling whatsoever during the entire spinning process.
The disadvantage of this known process is that the single fibers reach the spinning line in a more or less perpendicular position, so that the end of the forming yarn obtains at first a false twist, which must be reversed before a real twist is imparted. This results in yarn with an insufficient tear-resistance.
German published patent application 43 19 203 Al discloses that it is favorable when the single fibers are bound into the forming yarn to a great extent parallel to the spinning lines. In the known process this should be achieved in that single fibers, accelerated by an opening roller under the action of centrifugal forces, are accompanied in flight direction by an air current, which allegedly aligns the fibers parallel to the spinning line. It has been shown, however, that, using such pneumatic means, the fibers do not reach the spinning line in a parallel position, but rather more or less transversely thereto, so that in this process also, a larger false twist arises in the forming yarn.
German published patent application 1 510 937 discloses that the opened single fibers should be deposited on a transporting surface parallel to the spinning line. The publication is silent, however, as to how a sliver fed transversely to a transporting surface can be opened in such a way that the single fibers are disposed on the transporting surface in the desired direction.
It is an object of the present invention, based on a produced fiber veil of the above mentioned type, to feed the fibers in a controlled mechanical way to the spinning line in such a way that they extend to a great extent parallel to the spinning line, so that any modicum of false twist during yarn formation is as little as possible.
This object has been achieved in accordance with preferred embodiments of the present invention by providing that:
(a) at the transfer point the respective front part of the fiber veil is transferred as a fiber group at a predetermined sequence to the transporting surface; and PA1 (b) the transporting surface is moved transversely to the direction of motion of the collecting surface, so that the single fibers on the transporting surface are disposed transversely to the new direction of motion and thus essentially parallel to the spinning line.
Although the collecting surface as well as the transporting surface are each respectively moved at a continuous speed, the transfer of the single fibers from the collecting surface to the transporting surface takes place intermittently. The single fibers are transferred as fiber groups at regular intervals lasting a fraction of a second. This method permits each point of a single fiber to be released at the same time from the collecting surface and to reach the transporting surface. The single fibers are thus accelerated spontaneously in the new direction of motion, transverse to the old direction of motion, without the current relative angular orientation position of the single fibers being altered.
The length of the transfer point must, of course, be significantly longer than the staple length of the fibers to be spun. The sequenced transfer takes place always then, when the front part of the fiber veil, that is a fiber group, completely fills the space of the transfer point.
The speed of the transporting surface can determine the space between each of the single fibers, whereby the space should be so distinct that a purely open-end spinning arises.
In order that the single fibers adhere well to the collecting and transporting surfaces on the one hand, and on the other that this adherence can be eliminated immediately, the single fibers are held on the collecting surface and the transporting surface by means of suction.
It is favorable when, at the transfer point, the transporting surface which faces the collecting surface goes past the collecting surface while intersecting it at a small distance therefrom, whereby the sequenced fiber group to be transferred is lifted entirely from the collecting surface and disposed on the transporting surface. Plane surfaces are best suited for the collecting and transporting surfaces, for example a sieve belt or disk. Alternatively, a sieve drum would also be possible, as long as it had a sufficiently large diameter. The short distance permits a sufficiently rapid transfer, which lies in the range of milliseconds. The distance optimally measures between 3 and 4 mm. This permits a spontaneous change of direction to be set, without the relative position of the single fibers being altered, that is, the single fibers moving at first in their longitudinal direction are transported transversely to their longitudinal orientation within a fraction of a second.
It is purposeful when, during the sequenced transfer of a fiber group from the collecting surface to the transporting surface, the suction of the collecting surface in the area of the transfer point is temporarily discontinued. Thus the adherence in the area of the transfer point is abruptly and completely eliminated. The suction at the transfer point must, of course, be separate from the suction of the remaining areas of the collecting surface. The transporting surface in contrast can be continuously suctioned. The low pressure is maintained during the filling of the transfer point by a fiber group, and the low pressure is lifted for a fraction of a second, during the sequenced transfer of the single fibers from the collecting surface to the transporting surface.
In order to accelerate the transfer of the single fibers, the lifting of the fiber group from the collecting surface during the break in suction can be supported by means of compressed air.
It can be favorable when the fiber veil is already divided into fiber groups when it is being formed during opening of the sliver. Directly before the transfer point, a part of the collecting surface thus remains free of single fibers, or at least more fiber-free than in the other areas. This can be achieved by means of a controlled depositing of the single fibers on the collecting surface.
Furthermore, it is possible for the single fibers to be drawn again during the transfer of a fiber group from the collecting surface to the transporting surface. For example, the collecting surface and the transporting surface can be somewhat inclined towards each other, in such a way that the distance to the collecting surface in the direction of motion is somewhat enlarged. This ensures for certain that the fiber end reaches the transporting surface first, while the fiber head, due to its original direction of motion, still draws the relevant single fiber somewhat.
The process can be particularly easily executed if the transporting surface in the area of the spinning line is also effective in imparting a twist to the forming yarn. It is of course self-evident that a twist roller, and as desired, an air nozzle arranged downstream thereof are also effective in imparting the twist according to certain preferred embodiments.
Although it is desirable that the single fibers join the forming yarn as parallel to the spinning line as possible, it can be purposeful for the present invention when an additional false twist is imparted as a protective twist. The false twist should of course be very weak. This can be achieved by means of a slightly slantingly positioned twist roller, by means of which the arising fiber tip is strengthened, so that it cannot "hang" from the forming yarn. In any case, the false twist is removed after the yarn has left the transporting surface.